This application claims priority from PCT/US96/05270 filed Apr. 16, 1996 and from Israel patent application IL 113394 filed Apr. 17, 1995.
The present invention relates to nematicidal bacterial strains, and particularly to strains which affect plant-pathogenic nematodes. The invention also relates to agricultural nematicidal compositions as well as to methods of controlling plant pathogenic nematodes.
Root-knot is one of the most serious plant diseases in the world. Throughout the world, root-knot disease causes an average annual yield loss of about 5%. The greatest losses however, occur to those who can least afford it, namely, the farmers of underdeveloped countries. Their losses may be as much as 25-50% over a wide area of available farmland. In addition, there are several indirect losses associated with root-knot disease including secondary attack by other pathogens (in combination with other pathogens, root-knot disease can be disastrous); inefficient utilization of fertilizer and water; and high cost of chemical treatment.
The most common parasites causing this disease belong to the Meloidogyne spp. These nematodes have been shown to parasitize more than 3000 plant species including all the main crop families. Root-knot nematodes are found in all climate zones and in most types of soil. They are more active in finding and attacking plants in warm climates than in colder regions. Plants infected by root-knot nematodes display one or both of the following symptoms: root systems are galled, shortened or reduced by rotting; the stems are shortened and thickened, and the leaves do not grow normally.
The most distinctive symptom caused by root-knot nematodes are the galls or knots on the roots. The galls vary in size from a pin head to compound galls of more than 2.5 cm in diameter. They are irregular, spherical or spindle shaped and most often found on tender rootlets. These structures host one to several hundred female nematodes, which remain stationary throughout their life cycle and feed inside the root.
In light of their global economic impact on commercial crops, there is an urgent need to find an efficient way of controlling root-knot nematodes. Until now, chemicals such as methyl bromide or ethyl dibromide have been used to control nematodes. However, development of resistance by the pathogens to nematicidal chemicals, as well as a heightened awareness of short and long term ecological damage caused by these and other chemicals, have increased interest in developing a bio-nematicidal product which acts specifically against its target nematode without causing ecological damage.
It is an object of the present invention to provide bacterial strains having nematicidal activity against root-knot causing nematodes.
It is a further object of the present invention to provide an agricultural composition useful for protecting plants against root-knot nematodes.
It is an additional object of the present invention to provide a method of controlling plant-pathogenic nematodes.
In accordance with the present invention, new bacterial strains of the species B. firmus have been found which possess a nematicidal activity. These two bacterial strains are termed herein as Bacillus firmus strain CNCM I-1582 and Bacillus cereus strain CNCM I-1562. Both strains have been deposited with the Collection Nationale de Cultures de Microorganismes (CNCM), Institute Pasteur, France, at the following date and under the following Accession Nos.:
Use of the Bacillus firmus strain CNCM I-1582 and Bacillus cereus strain CNCM I-1562 strains is currently a preferred embodiment of the invention. Other strains useful in accordance with the present invention are various mutant strains derived from the Bacillus firmus strain CNCM I-1582 and Bacillus cereus strain CNCM I-1562 strains which possess nematicidal activity. Mutant strains are at times obtained spontaneously but can also be obtained by mutagenesis, e.g. by the use of irradiation or mutagens. As will be appreciated by the artisan, it is possible to induce various kinds of mutations which will not cause a substantial change in the bacteria""s nematicidal activity and their ability to exert this nematicidal activity when administered to soil in which the crops to be protected grow.
The present invention thus provides, by one of its aspects, a strain of bacteria belonging to the species B. firmus and possessing nematicidal activity, such strain being a member of the group consisting of EIP-N1 (CNCM I-1556), EIP-N2 (CNCM I-1562), and nematicidally active mutants of said Bacillus firmus strain CNCM I-1582 or Bacillus cereus strain CNCM I-1562.
Also provided by the present invention are pure cultures of bacteria, selected from the group consisting Bacillus firmus strain CNCM I-1582 or a Bacillus cereus strain CNCM I-1562 nematicidally active mutant of said Bacillus firmus strain CNCM I-1582 or Bacillus cereus strain CNCM I-1562.
According to another aspect of the present invention there is provided a nematicidal composition for use in plant protection comprising as active ingredient an effective amount of a nematicidal bacteria or of spores thereof, the bacteria being of a strain selected from the group consisting of Bacillus firmus strain CNCM I-1582 Bacillus cereus strain CNCM I-1562 and a nematicidally active mutant of said Bacillus firmus strain CNCM I-1582 or Bacillus cereus strain CNCM I-1562 together with a carrier compatible with the nematicidal bacteria.
In accordance with the preferred embodiment of the invention, the composition is supplemented by one or more supplements which improve or intensify the ability of the bacteria to exert their nematicidal activity. Supplements, may for example be nutrients such as gelatin, gelatin hydrolysate, cotton seed meal and casein hydrolysate.
According to another aspect of the present invention, there is provided a method for controlling plant-pathogenic nematodes, comprising applying to the plant roots or to the soil environment in which the plant grow, an effective amount of bacteria or spores thereof, the bacteria being of a strain selected from the group consisting of Bacillus firmus strain CNCM I-1582 Bacillus cereus strain CNCM I-1562 and a nematicidally active mutant of Bacillus firmus strain CNCM I-1582 or Bacillus cereus strain CNCM I-1562. The bacteria may be introduced into the soil by applying the bacteria under the soil within a liquid carrier. Alternatively, the bacteria may also be in a dry formulation and admixed with the soil, e.g. prior to planting or seeding. The bacteria may also be applied by impregnating plant roots or seeds prior to planting or seeding thereof into the soil, with a liquid formulation comprising the bacteria.
Another aspect of the present invention is a pot mix comprising bacteria of the invention.
The bacterial strains of the present invention are useful in controlling nematodes causing root-knot disease, and particularly those which belong to the Meloidogyne spp. However, the bacteria of the invention may also be effective against other pathogenic nematodes such as cyst nematodes.